Uneven coal burn in an EFM 520

I recently fired my EFM 520, it burns great for up to 12 hours. Then I notice the dark coal in the center starts expanding toward one side.About a 3'' wide strip of unburned coal reaches the edge and falls into the ashpit.I am running 6 teeth on the coal feed and between 5 and 6 on the air.
thanks in advance for your help, Bud

You might repost this in the manufacturers forum. But I'm sure answers will flow here, since you have fuel and heat I would guess it's an air problem, maybe the holes in the tulip that the coal and air mix in are pluged, EFM also seams to have a rod or lever for droping the ash out from the chamber below the grate or tulip.

Problem area might be visible in this link
Pictorial: The Burner Pot Assembly w/part numbers

Hi Bud, is this the first time you have used this unit? Sounds like a worn auger and/or a burner plate issue. I would start by shutting it down, and cleaning out the pot. Then you can inspect the different components. Check the auger for sharp edges, try and move it around to see how much play there is, make sure the burner plates are intact, and that the airflow isn't blocked with fines.

-Rob

Moved topic to the EFM forum.
Check for clogged holes or a damaged grate section or two. Did you pull the fines lever? Did it make a difference?

I'm with these guys. It's something wrong with the burner plate itself or a fines build-up underneath and possibly the worm, but not likely.